So with this logic every steel hulled/structure boat should sink right?

Did you even read my post and the one I was responding to? Floating is based on displacing water, not the weight of the material used to build the hole in the water.

Unless Tunnles is using something like a corrugated fiberglass core, (in which case he needs to stop saying solid fiberglass,) he has told the OP to make it thicker, and make it out of heavier material, and make it 66% lighter. That’s a neat trick. It also has nothing to do with the ability of the boat to float.